Liquid crystal display device

ABSTRACT

This invention reduces or prevents a phenomenon where a screen close to a light source becomes yellowed. A liquid crystal display device includes a liquid crystal display panel and a backlight. The backlight includes a light guide plate  10  and white LEDs  21  arrayed in a first direction on a plane of incidence  11  of the light guide plate  10 . The white LEDs  21  each includes, in the first direction on a light-emitting surface, a central area occupied by a blue spectrum more densely than at adjacent sides of the central area. Incident plane protrusions  111 , each extending in a thickness direction of the light guide plate  10 , are formed on a section corresponding to the area having the dense blue spectrum of each LED  21 , at the plane of incidence  11  of the light guide plate  10.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2014-217462 filed on Oct. 24, 2014, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to liquid crystal display devices thateach includes a backlight using light-emitting diodes (LEDs) as a lightsource, the liquid crystal display devices incorporating a preventivemeasure against color unevenness in the vicinity of the light source.

2. Description of the Related Art

Liquid crystal display devices include a thin-film transistor (TFT)substrate formed by elements such as pixel electrodes and TFTs, acounter substrate facing the TFT substrate, and liquid crystalssandwiched between the TFT substrate and the counter substrate. Thetransmittance of the light passing through the liquid crystal moleculesis controlled on a pixel-by-pixel basis to form an image.

Since the liquid crystals themselves do not emit light, a backlight isdisposed on a rear side of a liquid crystal display panel. Each of theliquid crystal display devices such as cellular phones uses LEDs as alight source for the backlight. The LEDs are arranged on a side surfaceof a light guide plate, various optical sheets are also arranged on thelight guide plate, and these optical parts are accommodated in amolding, thereby to configure the backlight. The method of arranging theLEDs on the side surface of the light guide plate is called the sidelight method.

The LEDs constitute a point light source, and the uniformity ofluminance in the backlight therefore is a vital factor. JP-A-2013-69498describes a configuration intended to obtain uniform luminance of abacklight by forming linear prismatic grooves on a lower surface of alight guide plate. JP-A-2013-93199 describes configurations of two kindsof grooved structures. One of the grooves structures is disposed on atleast one of a light-emitting surface and a counter surface of a lightguide plate. The other one having anisotropic diffusion characteristicsis on the light-receiving surface. These grooved structures enableuniform luminance of light from a backlight.

SUMMARY OF THE INVENTION

The configurations described in JP-A-2013-69498 and JP-A-2013-93199 bothintend to improve the uniformity of luminance in the respectivebacklights that use white LEDs. White LEDs are commonly used to obtainwhite light by placing a yellow fluorescent substance around an LED chipconfigured to emit high-energy light. In each backlight using theseLEDs, when a white color is displayed, an area in which the white colorhas shifted to yellow tends to occur in an area relatively close to thelight source. The present invention is intended to prevent this problem,that is, yellowing, from occurring.

Solution to Problem

An object of the present invention is to overcome the above problem,specifically by the following methods.

(1) A liquid crystal display device including a liquid crystal displaypanel and a backlight. The backlight includes a light guide plate andwhite LEDs arrayed in a first direction on a plane of incidence of thelight guide plate. The white LEDs each includes, in the first directionon a light-emitting surface, a central area occupied by a blue spectrummore densely than at its both sides. Incident plane protrusions, eachextending in a thickness direction of the light guide plate, are formedon a section corresponding to the area having the dense blue spectrum ofthe LEDs at the plane of incidence of the light guide plate.

(2) The liquid crystal display device described in above item (1),wherein an amount of light, refracted on the section corresponding tothe area having the dense blue spectrum of the LEDs at the plane ofincidence of the light guide plate, is larger than an amount of lightrefracted in any other areas of the light guide plate.

(3) The liquid crystal display device described in above item (1),wherein the area having the dense blue spectrum has a maximum “u′” valueof 0.4 on a CIE chromaticity diagram′

(4) A liquid crystal display device including a liquid crystal displaypanel and a backlight, the backlight including a light guide plate andwhite LEDs arrayed in a first direction on a plane of incidence of thelight guide plate. The white LEDs each includes on a light-emittingsurface: a first area occupied by a blue spectrum more densely than atadjacent sides of the first area in the center of the first direction onthe light-emitting surface; and a second area occupied by a yellowspectrum more densely than at adjacent sides of the second area in thefirst direction on the light-emitting surface than in the first area.First incident plane protrusions, each extending in a thicknessdirection of the light guide plate, are formed on a sectioncorresponding to the first area of each LED, at the plane of incidenceof the light guide plate; and second incident plane protrusions, eachextending in the thickness direction of the light guide plate, areformed on a section corresponding to the second area of the LED at theplane of incidence of the light guide plate. The first incident planeprotrusions are formed at pitches shorter than those of the secondincident plane protrusions.

(5) The liquid crystal display device described in above item (4),wherein the height of the first incident plane protrusions is greaterthan that of the second incident plane protrusions.

(6) A liquid crystal display device including a liquid crystal displaypanel and a backlight, the backlight including a light guide plate andwhite LEDs arrayed in a first direction on a plane of incidence of thelight guide plate. The white LEDs each includes on a light-emittingsurface: a first area occupied by a blue spectrum more densely than atadjacent sides of the first area in the center of the first direction onthe light-emitting surface; and a second area occupied by a yellowspectrum more densely than at adjacent sides of the second area in thefirst direction on the light-emitting surface than in the first area.First incident plane protrusions, each extending in a thicknessdirection of the light guide plate, are formed on a sectioncorresponding to the first area of each LED at the plane of incidence ofthe light guide plate; and second incident plane protrusions, eachextending in the thickness direction of the light guide plate, areformed on a section corresponding to the second area of the LED at theplane of incidence of the light guide plate. The height of the firstincident plane protrusions is greater than that of the second incidentplane protrusions.

(7) The liquid crystal display device described in above item (6),wherein a pitch of the first incident plane protrusions is the same asthat of the second incident plane protrusions.

(8) The liquid crystal display device described in any one of items (4)to (7), wherein the area having the dense blue spectrum has a maximum“u′” value of 0.4 on a CIE chromaticity diagram.

(9) The liquid crystal display device described in any one of items (1)to (8), wherein the incident plane protrusions are arc-shaped incross-sectional profile on a surface parallel to a principal plane ofthe light guide plate.

(10) The liquid crystal display device described in any one of items (1)to (8), wherein the incident plane protrusions are triangular incross-sectional profile on a surface parallel to a principal plane ofthe light guide plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a liquid crystal displaydevice;

FIG. 2 is a perspective view of a backlight;

FIG. 3 is a schematic plan view that shows yellowing of a screen;

FIG. 4 is a perspective view of a light guide plate;

FIG. 5 is a cross-sectional view of section A-A shown in FIG. 4;

FIG. 6 is a cross-sectional view of section B-B shown in FIG. 4;

FIG. 7 is a perspective view of an LED;

FIG. 8 is a CIE 1976 UCS chromaticity diagram;

FIG. 9 is a graph that shows changes in u′ value on a light-emittingsurface of the LED;

FIG. 10 is a graph that shows changes in v′ value on the light-emittingsurface of the LED;

FIG. 11 is a cross-sectional view showing a configuration of the LED;

FIG. 12 is a plan view showing a reflecting surface of the light guideplate, the plan view also serving as a schematic diagram to show anoptical path of incident light beams;

FIG. 13 is a perspective view that shows layout of the light guide plateand the LED;

FIG. 14 is a plan view showing a positional relationship between an LEDand light guide plate in a conventional example;

FIG. 15A is a plan view showing a positional relationship between an LEDand light guide plate in a first embodiment of the present invention;

FIG. 15B is an enlarged plan view of FIG. 15A;

FIG. 15C is a perspective view that shows protrusions present on a planeof incidence;

FIG. 16A is a plan view showing a positional relationship between an LEDand light guide plate in a second embodiment of the present invention;

FIG. 16B is an enlarged plan view of FIG. 16A;

FIG. 17A is a plan view showing a positional relationship between an LEDand light guide plate in a third embodiment of the present invention;

FIG. 17B is an enlarged plan view of FIG. 17A;

FIG. 18A is a plan view showing a positional relationship between an LEDand light guide plate in a fourth embodiment of the present invention;

FIG. 18B is an enlarged plan view of FIG. 18A;

FIG. 18C is a comparative view showing, for comparison, differentprotrusions present on a plane of incidence;

FIG. 19 is an enlarged plan view showing a positional relationshipbetween an LED and light guide plate in a fifth embodiment of thepresent invention;

FIG. 20A is a plan view showing a positional relationship between an LEDand light guide plate in a sixth embodiment of the present invention;and

FIG. 20B is an enlarged plan view of FIG. 20A.

DESCRIPTION OF EMBODIMENTS

The present invention will be described in detail below with referenceto embodiments thereof.

First Embodiment

FIG. 1 is a schematic cross-sectional view of a liquid crystal displaydevice. The liquid crystal display device includes a liquid crystaldisplay panel 300 and a backlight 400. The liquid crystal display panel300 includes: a TFT substrate 100 on which pixels, having TFTs and pixelelectrodes, are formed in a matrix format; a counter substrate 200 whichis positioned opposite to the TFT substrate 100; liquid crystals whichare sandwiched between the TFT substrate 100 and the counter substrate200; a lower polarizer 101 which is attached to the TFT substrate 100;and an upper polarizer 201 which is attached to the counter substrate200. The backlight 400 is disposed on a rear side of the liquid crystaldisplay panel 300.

FIG. 2 is a perspective view showing a configuration of the backlight400. Referring to FIG. 2, a light source 20 with LEDs is disposed on aside surface of a light guide plate 10. A flexible wiring substrate 27for light sources is connected to the light source 20. A reflectingsheet 30 for directing light toward the liquid crystal display panel isplaced on a lower surface of the light guide plate 10. A diffusing sheet40 for diffusing the light uniformly is placed on the light guide plate10. A lower prismatic sheet 50, with a large number of linear prismaticstructures formed in a specific direction on the sheet, is disposed onthe diffusing sheet 40. And an upper prismatic sheet 60, with a largenumber of linear prismatic structures formed in a directionperpendicular to the specific direction on the sheet 60, is disposed onthe lower prismatic sheet 50. The lower prismatic sheet 50 and the upperprismatic sheet 60 perform the function of directing in a directionnormal to the liquid crystal display panel 300 the light incident in anoblique direction relative to the liquid crystal display panel 300,thereby raising the efficiency in the use of the light coming in fromthe backlight. A light-blocking sheet 70 for blocking out the light thatmay propagate to the periphery of the screen of the liquid crystaldisplay panel is formed in a shape of a frame on the upper prismaticsheet 60. The optical parts described above are accommodated in a resinmolding 80.

FIG. 3 is a schematic plan view representing a problem associated with adisplay screen 500 of a liquid crystal display panel employed in aconventional example. Referring to FIG. 3, a light source 20 with LEDsis disposed near a side surface of the display region on the liquidcrystal display panel. During display of a white color on the screen500, there is a yellowish area on the light source side of the displayregion. This area is referred to as a yellowing area 510. The followingdescribes the yellowing event.

FIG. 4 is a perspective view of the light guide plate 10. One side 11 ofthe light guide plate 10 functions as a plane of incidence, and an uppersurface of the light guide plate 10 functions as an exit surface 12. Onthe exit surface 12, such linear protrusions 121 as denoted by referencenumber 121 in FIG. 4 extend in an x-direction, and these protrusions arearrayed in a y-direction. The lower surface of the light guide plate 10serves as a plane of reflection, on which such linear protrusions 131 asrepresented by a dotted line 131 in FIG. 4 extend in the y-direction,and these protrusions are arrayed in the x-direction. The thickness ofthe light guide plate 10 ranges, for example, from 0.3 to 0.5 mm. Thelight guide plate 10 is made from a transparent or translucent resin,such as acryl or polycarbonate.

FIG. 5 is a cross-sectional view of section A-A shown in FIG. 4. Asshown in FIG. 5, the LEDs 21, or the light source, that face the planeof incidence of the light guide plate 10 are disposed as represented bya dotted line. The linear protrusions 121 with height h1 are formed atpitches p1 on the upper surface of the light guide plate 10. The lengthof each pitch p1 is 100 μm, for example. The height of each linearprotrusion 121 is smallest at the portion closest to the LEDs, andincreases with longer distance from the LEDs. The height h1 of eachlinear protrusion 121 is, for example, 0.1 μm at the portion closest tothe LEDs, and 10 μm at the portion farthest therefrom. Upper linearprotrusions 121 have, for example, substantially the same triangularcross-sectional shape as that of a linear prism.

FIG. 6 is a cross-sectional view of section B-B shown in FIG. 4. On thelower surface, that is, reflecting surface 13, of the light guide plate10, lower linear protrusions 131 are formed at pitches p2 and withheight h2. The length of each pitch p2 is 100 μm, for example, and theheight h2 is constant and is, for example, 10 μm. Unlike the upperlinear protrusions 121, the lower linear protrusions 131 are, forexample, arc-shaped or barrel-shaped in cross-sectional profile.

FIG. 7 is a perspective view showing a shape of one of the LEDs 20.Width w1 of a light-emitting surface on the LED 20 is, for example, 3.0mm, and package width w3 of the LED 20 is, for example, 3.8 mm. Anelectrode 25 for supplying an electric current to an LED chip is formedon adjacent sides of the LED 21. FIG. 7 shows a white LED, and this LEDis designed to emit white light. When a luminous spectrum developed onthe light-emitting surface 24 is measured in detail along a dotted lineshown in FIG. 7, however, the spectrum of the LED 21 is mainly occupiedby blue at around the central area of the LED, and is mainly occupied byyellow at adjacent sides of the central area. The area shown as B inFIG. 7 denotes the one where blue predominates, and that shown as Ydenotes the one where yellow predominates. Width w2 of the area whereblue predominates is 1 mm, for example.

FIG. 8 is a CIE 1976 UCS chromaticity diagram. As shown in FIG. 8, ahorizontal axis denotes u′ and a vertical axis denotes v′. FIG. 8 showsthat as v′ increases, the light assumes a more yellowish color, and thatas v′ decreases, the light assumes a more bluish color.

FIG. 9 is a representation of changes in the u′ value as measured alongthe dotted line across the light-emitting surface in FIG. 7, and FIG. 10is a representation of changes in the v′ value as measured along thedotted line across on the light-emitting surface in FIG. 7. As shown inFIG. 9, u′ undergoes only minimal changes. In contrast to this, v′decreases in its horizontal data range of ±0.5 mm across the center ofthe light-emitting surface. This area corresponds to an area in which v′is smaller than 0.4. In other words, in this area, blue is relativelypredominant, compared to other areas of the light-emitting surface, andyellow is predominant at adjacent sides of the area.

This color distribution is considered to be due to such a configurationof the LED 21 that is shown in FIG. 11. FIG. 11 is a cross-sectionalview of the LED 21, taken along a surface parallel to a principal planeof the light guide plate. The LED package in FIG. 11 contains the LEDchip 22 that is surrounded with a yellow fluorescent substance 23. Bluelight emissions from the LED chip 22 are subject to color conversion bythe fluorescent substance, thus becoming white light as a whole. Whenthe light is microscopically viewed, however, its chromaticity slightlyvaries from location to location on the light-emitting surface.

Referring to FIG. 11, the light emitted directly to above the LED chip22, that is, in a direction normal to the light-emitting surface, willassume a slightly bluish color rather than a white color, since thelight will only be color-converted at a short distance by the yellowfluorescent substance 23. The light emitted in a direction that forms anangle with the direction normal to the light-emitting surface willassume a slightly yellowish color rather than a white color, since thelight will be color-converted at a long distance by yellow fluorescentsubstance 23.

FIG. 12 is a schematic plan view showing a path that such LED light asshown in FIG. 11 travels after entering the light guide plate 10. Sincethe bluish light B that has been emitted in the direction normal to thelight-emitting surface of the LED enters the plane of incidence of thelight guide plate 10 vertically, the bluish light B travels straightahead and goes a longer distance inside the light guide plate 10. Bycontrast, the light emitted at a certain angle with respect to thedirection normal to the light-emitting surface of the LED is most likelyto stay in a greater amount near the light source after being reflectedor scattered by the reflecting surface protrusions 131 or the like. Inthe area close to the light source, therefore, the light emitted fromthe light guide plate 10 is more yellowish than in other areas. Thisevent is considered to cause yellowish color unevenness on the lightsource side of the screen in the conventional example.

FIG. 13 is a perspective view that shows exemplary layout of a lightguide plate 10 and LEDs 21 serving as a light source. The LEDs 21 inFIG. 13 are arranged at pitches p3 in an x-direction along a plane ofincidence 11 on the light guide plate 10. The pitches p3 range, forexample, between 5 and 10 mm. Width w3 of the LEDs 21, in thex-direction, corresponds to the width of the LED package shown in FIG.7. The width w3 is, for example, 3.8 mm. Light that has entered thelight guide plate 10 exits from an exit surface 12 and travels toward aliquid crystal display panel disposed above. By contrast, light headingdownward from the light guide plate 10 is reflected by a reflectingsheet 30 and then directed toward the exit surface 12.

FIG. 14 is an enlarged plan view showing a positional relationshipbetween the light guide plate 10 and LED 21 in the conventional example.While an ideal distance between the LED 21 and the light guide plate 10is zero, there actually is a slight distance due to manufacturingvariations in products. The LED configuration is as described in FIG.11. In the conventional example, as shown in FIG. 12, yellowish lightdue to the reflection or scattering inside the light guide plate 10 ispresent in a large amount near the LED, hence causing the yellowing ofthe screen.

FIG. 15A is a plan view showing a positional relationship between an LED21 and light guide plate 10 in the first embodiment of the presentinvention. The LED 21 has the same configuration as that described inFIG. 11. LED 21 configurations in a second and subsequent embodiments ofthe present invention are also the same as the LED 21 configuration ofFIG. 11. As shown in FIG. 15A, incident plane protrusions 111 are formedon a plane of incidence of the light guide plate that corresponds to thearea where a blue color predominates in the LED 21. These protrusionsare disposed to scatter bluish light. The protrusions 111 are providedin association with the area where v′ in FIG. 10 is smaller than 0.4.This means that if the LED 21 corresponding to FIG. 10 is used, the areawhere blue predominates will be formed in a horizontal data range of±0.5 mm across the central area of the LED 21.

The width of the area where v′ in FIG. 10 is smaller than 0.4 may beexpressed as w2. Even if the incident plane protrusions 111 are formedin an area narrower than w2, the liquid crystal display device accordingto the present embodiment will still be effective to a certain degree.In addition, while it has been described as per FIG. 10 that the bluisharea is where v′ is smaller than or equal to 0.4, the value is notlimited to 0.4. If part of the central area is smaller in magnitude ofthe v′ value than on adjacent sides of the central area, the liquidcrystal display device according to the present embodiment will still beeffective to a certain degree by forming incident plane protrusions 111on the plane of incidence of the light guide plate 10 so as to make theincident plane protrusions 111 correspond to that part.

FIG. 15B is an enlarged plan view showing a shape of the incident planeprotrusions 111 on the plane of incidence of the light guide plate 10 inFIG. 15A. Height h4 of the incident plane protrusions 111 in FIG. 15Bis, for example, 5 μm, and pitch p4 of the incident plane protrusions111 is, for example, 20 μm. The incident plane protrusions 111 are, forexample, arc-shaped or barrel-shaped in cross-sectional profile on asurface parallel to a principal plane of the light guide plate. Onlyfour incident plane protrusions are formed in FIG. 15B. However, alarger number of protrusions, nearly 50 pieces for example, are formedin practice.

FIG. 15C is a perspective view of the area in which the incident planeprotrusions 111 on the plane of incidence 11 of the light guide plate 10are formed. The incident plane protrusions 111 are formed linearly atthe pitches p4 over the entire thickness direction of the light guideplate 10. While incident plane protrusions 111 in a second andsubsequent embodiments of the present invention will only be describedin plan view, these incident plane protrusions 111 are formed linearlyover the entire thickness direction of a light guide plate 10, as withthe protrusions of FIG. 15C.

As set forth above, in accordance with the present embodiment, theoccurrence of yellowing near the light source can be mitigated since theincident plane protrusions 11 on the light guide plate 10 refract thebluish light that the LED 21 has emitted primarily from around thecentral area of the light-emitting surface.

Second Embodiment

FIG. 16A is a plan view showing a positional relationship between an LED21 and light guide plate 10 in the second embodiment of the presentinvention. The LED 21 has substantially the same configuration as thatdescribed in FIG. 11. As shown in FIG. 16A, incident plane protrusions111 are formed on the plane of incidence of the light guide plate thatcorresponds to the area where blue predominates in the LED 21. Thepresent embodiment differs from the first embodiment in that theincident plane protrusions 111 are prismatic or triangular incross-sectional profile on a surface parallel to a principal plane ofthe light guide plate. Other configurational aspects are substantiallythe same as in FIG. 1.

FIG. 16B is an enlarged plan view showing a shape of the incident planeprotrusions 111 formed on the plane of incidence 11 of the light guideplate 10 in FIG. 16A. Height h4 of the incident plane protrusions 111 inFIG. 16B is, for example, 5 μm, and pitch p4 of the incident planeprotrusions 111 is, for example, 20 μm. That is to say, the height h4and the pitch p4 are the same as in the first embodiment. The incidentplane protrusions 111 are typically 90 degrees in apex angle θ. Thisangle is set to be 90 degrees to obtain incident light refractioncharacteristics and for a reason of the ease of manufacturing of theincident plane protrusions, but the liquid crystal display deviceaccording to the present embodiment still offers the advantageouseffects with other angles.

As set forth above, in accordance with the present embodiment, theoccurrence of yellowing near the light source can be mitigated since theincident plane protrusions 111 on the light guide plate 10 refract thebluish light that the LED 21 has been emitted primarily from around thecentral area of the light-emitting surface.

Third Embodiment

FIG. 17A is a plan view showing a positional relationship between an LED21 and light guide plate 10 in a third embodiment of the presentinvention. The LED 21 has substantially the same configuration as thatdescribed in FIG. 11. As shown in FIG. 17A, on those sections of theplane of incidence 11 of the light guide plate 10 that correspond to theLED area, incident plane protrusions 111 are formed in both the areawhere a blue color predominates and the area where a yellow colorpredominates. The incident plane protrusions 111 on the sectioncorresponding to the area where blue predominates, however, are formedat pitches shorter than those of the incident plane protrusions 111formed on the section corresponding to the area where yellowpredominates. Briefly, the density of the incident plane protrusions 111in the former of the two areas is higher than in the latter. This meansthat on the section where blue predominates, a greater amount of lightis refracted and scattered than on other sections, so that there is agreater amount of blue in an area close to the light source.

FIG. 17B is an enlarged plan view showing a shape of the incident planeprotrusions 111 formed on the plane of incidence of the light guideplate 10 in FIG. 17A. As shown in FIG. 17B, the incident planeprotrusions 111 on the section of the light guide plate 10 thatcorresponds to the LED area where blue predominates are formed atpitches p5. The incident plane protrusions 111 on the section of thelight guide plate 10 that corresponds to the LED area where yellowpredominates are formed at pitches p6. And in this case, p5<p6 holds. Inother words, on the section of the light guide plate 10 that correspondsto the LED area where blue predominates, the incident plane protrusions111 are formed at a density higher than in other areas. The height ofthe incident plane protrusions 111 is shown as h5, which is the same forboth the section where blue predominates and the section where yellowpredominates. The values of p5, p6, and h5 are, for example, 20 μm, 40μm, and 5 μm, respectively.

Referring to FIG. 17B, only three incident plane protrusions 111 areformed in the LED area where blue predominates. However, a larger numberof protrusions, nearly 50 pieces for example, are formed in practice.The incident plane protrusions 111 in FIGS. 17A and 17B are arc-shapedin cross-sectional profile, but the protrusions do not always need tohave the shape of an arc. Instead, they may have such a prismatic shapethat is shown in the second embodiment.

As set forth above, in accordance with the third embodiment, theincident plane protrusions 111 on the section of the light guide plate10 that corresponds to a specific area of the LED 21 are formed at adensity higher than at any other sections. The bluish light emitted froman area close to the central area of the light-emitting surface is thusrefracted or scattered in a greater amount, so that the occurrence ofyellowing near the light source is mitigated.

Fourth Embodiment

FIG. 18A is a plan view showing a positional relationship between an LED21 and light guide plate 10 in a fourth embodiment of the presentinvention. The LED 21 has substantially the same configuration as thatdescribed in FIG. 11. As shown in FIG. 18A, on those sections of theplane of incidence 11 of the light guide plate 10 that correspond to theLED areas, incident plane protrusions 111 are formed in both of the areawhere a blue color predominates and the area where a yellow colorpredominates. The height of the incident plane protrusions 111 on thesection corresponding to the area where blue predominates in the LED 21,however, is greater than that of the incident plane protrusions 111formed on the section corresponding to the area where yellowpredominates in the LED 21. Such a shape of the protrusions increasesthe refraction or scattering of the light on the section where bluepredominates.

FIG. 18B is an enlarged plan view showing a shape of the incident planeprotrusions 111 formed on the plane of incidence of the light guideplate 10 in FIG. 18A. As shown in FIG. 18B, the incident planeprotrusions 111 on the section of the light guide plate 10 thatcorresponds to the area where blue predominates in the LED 21 are formedat pitches p7, and the incident plane protrusions 111 on the section ofthe light guide plate 10 that correspond to the area where yellowpredominates in the LED 21 are also formed at the pitches p7. However,height h7 of the incident plane protrusions 111 on the section of thelight guide plate 10 that corresponds to the area where bluepredominates in the LED 21 is greater than height h8 of the incidentplane protrusions 111 formed on the section of the light guide plate 10that corresponds to the area where yellow predominates in the LED 21.The pitches p7 of the incident plane protrusions 111 are, for example,20 μm, the height h7 is, for example, 3 μm, and the height h8 is, forexample, 1 μm.

FIG. 18C is a cross-sectional comparative view of two incident planeprotrusions 111 that differ in height. As shown in FIG. 18C, even if thetwo incident plane protrusions 111 have the same width, the one that isgreater in height tends to be smaller in a radius of curvature of theincident plane protrusion, so that this protrusion refracts or scattersincident light in a greater amount.

As set forth above, in accordance with the present embodiment, since theheight of the incident plane protrusions 111 formed on the section ofthe light guide plate 10 that corresponds to a specific area in the LED21 is greater than the height of other sections, the bluish lightemitted from an area close to a central area of the light-emittingsurface on the LED 21 will be refracted or scattered in a greateramount, so that the occurrence of yellowing near the light source ismitigated.

Fifth Embodiment

FIG. 19 is a plan view showing a section of a light guide plate 10 thatcorresponds to a light-emitting surface of an LED 21 in a fifthembodiment of the present invention. The present embodiment has aconfiguration that incorporates features of both the third and fourthembodiments. As shown in FIG. 19, on those sections of the plane ofincidence 11 of a light guide plate 10 that correspond to areas of theLED 21, incident plane protrusions 111 are formed in both of the areawhere a yellow color predominates and the area where a blue colorpredominates. The incident plane protrusions 111 on the sectioncorresponding to the LED area where blue predominates, however, aregreater in height and shorter in pitch than the incident planeprotrusions 111 on the section corresponding to the LED area whereyellow predominates. Height h7 of the incident plane protrusions 111 onthe section corresponding to the LED area where blue predominates is,for example, 3 μm, and pitch p7 is, for example, 20 μm. Height h8 of theincident plane protrusions 111 on the section corresponding to the LEDarea where yellow predominates is, for example, 1 μm, and pitch p8 is,for example, 40 μm.

As set forth above, in accordance with the present embodiment, theheight of the incident plane protrusions 111 formed on the section ofthe light guide plate 10 that corresponds to a specific area in the LED21 is greater than that of other sections, and the pitch of theseincident plane protrusions is shorter than that of the other sections.Accordingly the bluish light emitted from around the central area of thelight-emitting surface on the LED 21 is refracted or scattered in agreater amount, so that the occurrence of yellowing near the lightsource is mitigated.

Sixth Embodiment

FIG. 20A is a plan view showing a positional relationship between an LED21 and light guide plate 10 in a sixth embodiment of the presentinvention. The LED 21 has substantially the same configuration as thatdescribed in FIG. 11. As shown in FIG. 20A, on those sections of theplane of incidence 11 of the light guide plate 10 that correspond tospecific areas of the LED 21, incident plane protrusions 111 are formedin both of the area where a blue color predominates and the area where ayellow color predominates. While the height of the incident planeprotrusions 111 is greater at the section corresponding to the areawhere blue predominates in the LED 21, the height of these incidentplane protrusions 111 progressively diminishes with decreasing distancewith respect to the area where yellow predominates. The pitches of theincident plane protrusions 111 are the same for both the area where bluepredominates and the area where yellow predominates.

FIG. 20B is an enlarged plan view of the light guide plate 10 with thesections corresponding to a light-emitting area of the LED 21, the planview showing an exemplary layout of the above two sets of incident planeprotrusions. As shown in FIG. 20B, the height of the incident planeprotrusions 111 in the area where blue predominates is shown as h10, theheight of the incident plane protrusions 111 in the area where yellowpredominates is shown as h12, and the height of other incident planeprotrusions 111 present in between the former two sets of incident planeprotrusions 111 is shown as h11. The height h11 is of the incident planeprotrusions 111 present at a boundary of the area where bluepredominates and the area where yellow predominates. The pitch of theincident plane protrusions 111 in FIG. 20B is constant, which is 20 μm,for example. The height h10 of the incident plane protrusions 111 is 3μm, the height h11 is 2 μm, and the height h12 is 1 μm, for example.

Referring to FIG. 20A, the height h10 of the incident plane protrusions111 is constant at the area where blue predominates, and progressivelydiminishes to a level of h12 at the area where yellow predominates. Inthe central area where blue predominates, however, the height of theincident plane protrusions may be set as the greatest height h10 of thethree heights, and may also progressively diminish to the level of h12at an outer edge of the area where yellow predominates. In this way, theheight of the protrusions may be continuously changed.

As set forth above, in accordance with the present embodiment, theoccurrence of yellowing near the light source can be mitigated since atthe plane of incidence 11 of the light guide plate 10, bluish light thatthe LED 21 emits is refracted or scattered in a greater amount thanyellowish light.

While the incident plane protrusions in the fourth to sixth embodimentsare arc-shaped in cross-sectional profile, the shape of the incidentplane protrusions may be triangular or prismatic, as in the secondembodiment.

What is claimed is:
 1. A backlight comprising: a light guide plateincluding an incident surface, and a plurality of LEDs arrayed in afirst direction and opposed to the incident surface, wherein theplurality of LEDs each includes, in the first direction in alight-emitting surface, a first area occupied by a blue spectrum moredensely than at its both sides, the light guide plate has protrusionseach projecting in a direction that is perpendicular to a thicknessdirection of the light guide plate at the incident surface, a firstgroup of protrusions is formed corresponding to the first area of theLEDs, a second group of protrusions is formed corresponding to bothsides of the first area, and a pitch of the protrusions of the firstgroup is shorter than that of the protrusions of the second group. 2.The backlight according to claim 1, wherein the height of theprotrusions in the first area is greater than that of the protrusions inthe both sides of the first area.
 3. The backlight according to claim 1,wherein an amount of light of the first area is larger than that of bothsides of the first area.
 4. The backlight according to claim 1, whereinthe blue spectrum has an “u′” value equal to or less than 0.4 on a CIEchromaticity diagram in the first area.
 5. The backlight according toclaim 1, wherein the protrusions are arc-shaped in cross-sectionalprofile on a surface parallel to a principal plane of the light guideplate.
 6. The backlight according to claim 1, wherein the protrusionsare triangular in cross-sectional profile on a surface parallel to aprincipal plane of the light guide plate.
 7. A backlight comprising: alight guide plate including an incident surface, a plurality of LEDs,arrayed in a first direction, oppose to the incident surface, theplurality of LEDs each having a light-emitting surface: a first area,which is in a center in the first direction of the light-emittingsurface, having a blue spectrum more densely than at a second area,which occupies adjacent sides to the first area; and the second area hasa yellow spectrum more densely than at the first area, wherein firstincident surface protrusions, each projecting in a direction that isperpendicular to a thickness direction of the light guide plate, areformed on a section corresponding to the first area of each of theplurality of the LEDs, at the incident surface of the light guide plate,second incident surface protrusions, each projecting in the directionthat is perpendicular to the thickness direction of the light guideplate, are formed on a section corresponding to the second area of eachof the plurality of LEDs, at the incident surface of the light guideplate, and the first incident surface protrusions are formed in pitchesshorter than those of the second incident surface protrusions.
 8. Thebacklight according to claim 7, wherein the height of the first incidentsurface protrusions is greater than that of the second incident surfaceprotrusions.
 9. The backlight according to claim 7, wherein the bluespectrum has an “u′” value equal to or less than 0.4 on a CIEchromaticity diagram in the first area.
 10. The backlight according toclaim 7, wherein the incident surface protrusions are arc-shaped incross-sectional profile on a surface parallel to a principal plane ofthe light guide plate.
 11. The backlight according to claim 7 whereinthe incident surface protrusions are triangular in cross-sectionalprofile on a surface parallel to a principal plane of the light guideplate.
 12. A backlight comprising: a light guide plate including anincident surface, a plurality of white LEDs, arrayed in a firstdirection, oppose to the incident surface, the white LEDs each having alight-emitting surface: a first area, which is in a center in the firstdirection of the light-emitting surface, having a blue spectrum moredensely than at a second area, which occupies adjacent sides to thefirst area; and the second area has a yellow spectrum more densely thanat the first area, wherein first incident surface protrusions, eachprojecting in a direction that is perpendicular to a thickness directionof the light guide plate, are formed on a section corresponding to thefirst area of each of the plurality of the LEDs, at the incident surfaceof the light guide plate, second incident surface protrusions, eachprojecting in the direction that is perpendicular to the thicknessdirection of the light guide plate, are formed on a sectioncorresponding to the second area of each of the plurality of LEDs, atthe incident surface of the light guide plate, and the height of thefirst incident surface protrusions is greater than that of the secondincident surface protrusions.
 13. The backlight according to claim 12,wherein the blue spectrum has an “u′” value equal to or less than 0.4 ona CIE chromaticity diagram in the first area.
 14. The backlightaccording to claim 12, wherein the first incident surface protrusionsare arc-shaped in cross-sectional profile on a surface parallel to aprincipal plane of the light guide plate.
 15. The backlight according toclaim 12, wherein the incident surface protrusions are triangular incross-sectional profile on a surface parallel to a principal plane ofthe light guide plate.